The WIG crafts use the ground effect that when the wing of a flying vehicle flies near the ground (or the water surface), the descent airflow gets to be screened by the ground (or the water surface), and thereby, the lift force gets to be increased and the drag gets to be decreased. Most modern high speed marine crafts have lift-to-drag ratios (L/D) of below 10 and most airplanes have lift-to-drag ratios of 10˜20. In comparison with them, the wig crafts using the ground effect can have lift-to-drag ratios of as high as 20˜30. Thus, the wig crafts have high fuel efficiency and can fly at the speed of general propeller aircrafts without being in direct contact with the water.
The WIG craft having such features can perform various roles in the middle field between boats and airplanes, and the WIG craft born for a low-level flight only is classified as a boat by the International Maritime Organization.
In 1960's, the early models of the wig crafts, the X-112 made by Alexander Lippisch and the SM-2P made by Rostislav Alexeiev flew successfully. Since then, many studies on the WIG craft have been performed and as a result, various types of the WIG crafts have appeared, for examples, the reversed delta wing type (i.e. FS-8, X-114, Hover-Wing, etc.); the Ekranoplan type (i.e. KM, Orlyonok, etc.); the tandem type (i.e. Joerg tandem, etc.); the ram wing type (i.e. KAG-3, Volga-2, Amphistar, etc.); the canard type (i.e. Kaien series of TOTTORI University, etc).
The Joerg tandem wig craft, one of the prior wig crafts, is illustrated in FIGS. 1 and 2. The wig craft comprises: a body 100; a front wing 200 having an aspect ratio of 1˜1.5 as positioned in the low front side of the body; a rear wing 300 having almost the same area and the same span as the front wing, which is positioned a little apart in the rear with the same level as the front wing; a right end plate and a left end plate 600 connecting the end of the front wing with that of the rear wing respectively; a propeller 400 in the rear of the body 100; a vertical stabilizer 320; and a rudder 321.
The way how to fly the WIG craft is explained as follows. When thrust is generated by the propeller, the body and the wings, which were partly immersed under the water surface providing buoyancy at rest, rise onto the water surface by hydrodynamic lift and then the WIG craft starts to plane. As its speed goes higher, the aerodynamic lift in ground effect gets to be increased. And when it has accelerated enough, the WIG craft rises above the water surface and continues to cruise. When the WIG craft gets to fly higher, the aerodynamic lift of the wings of small aspect ratios gets to be decreased rapidly due to the weakened ground effect, and the front wing and the rear wing maintain their height and attitude through the ground effects on fore and rear, and right and left sides. Since the said wings have no elevator, the WIG craft's cruising height and speed get to be determined by thrust. Meanwhile, the WIG craft cannot fly high up in the air due to the stability problem.